The practical objects and aspects of the invention, in a large degree, relate to avoidance of certain well-known drawbacks of engines of the Day type, exemplified by the common "two-port" and "three-port," in designing engines of comparable simplicity and compactness. Space-wise, progress in that area is the major subject of the disclosure, discussed in detail with illustrated example, which, however, makes it obvious that a principle of more general applicability has been evolved, defining a new class of two-stroke combustion-engines. The specification and appended claims reflect that situation, but in conveying the basic spirit of the invention it is believed appropriate to concentrate upon comparison of one form of my engine with Day's version, so well known commercially. Doubling the length of a gas flow path in a "return-flue" steam-boiler is analagous, perhaps, to the idea of partitioning a combustion-engine cylinder for return-flow, the longer path affording enhanced stratification of old and new gas contents. An annular partition or divider is, of course, preferred for practical reasons. This new element--not a moving-part--is referred to as a water-cell or sleeve, and its incorporation in a Day-type engine entails elongation of the piston and additional machined-surfaces, besides a commitment to water-cooling and extra gas-seals. The result, however, which seems to be novel in spite of very extensive prior-art, indicates that significant domestication of the two-stroke carbureted gasoline-engine, at least, can be achieved, probably to an extent that, for many purposes, as the automotive field, the four-stroke engine can be supplanted. The partitioning-concept embodied in the example, in a crankcase-compression context, is clearly independent of the means of supplying scavenging-material to the open-end of the modified trunk-type piston, the salient feature being the axisymmetric scavenging-flow pattern which is effected, charge-wasting associated with the Day's transverse scavenging or with poorly-stratified uniflow-scavenging being avoided. With the gasoline-engine proposed in the example, piston overheating and distortion due to uneven cooling is avoided, allowing better lubrication and extending usefulness, vane-like transfer-porting lands in the piston functioning as a heat-exchanger. Owing to position of spark-plug electrodes relative to scavenging-circuit, and pronounced stratification of cylinder-contents after compression, misfiring and rough idling with partial-charges should be drastically reduced, perhaps no worse than that of a four-stroke. Below the level of the wrist-pin at end of down-stroke, this form of my engine is similar to commercial types.